This invention relates to a process for the preparation of polyurethane urea elastomers. More specifically it relates to such a process in which an aromatic diamine containing sulfonic acid amide group is used as a chain lengthening agent.
The production of polyurethane urea elastomers from polyisocyanates, relatively high molecular weight polyhydroxyl compounds and aromatic diamines is known. In order to achieve acceptable processing times, the commonly used reactive aromatic isocyanates are reacted with diamines which are relatively insert. Suitable diamines are those aromatic diamines in which the basicity (and hence also the isocyanate reactivity) has been reduced by the introduction of halogen or carboxyl substituents. The most commonly used diamines are 3,3'-dichloro-4,4'-diaminodiphenylmethane (MOCA) and 4-chloro-3,5-diaminobenzoic acid isobutylester.
In U.S. Pat. No. 3,891,606 one such method for producing polyurethane urea elastomers is described. In this patented process, an isocyanate prepolymer is made from polyhydroxyl compounds and an excess of polyisocyanates. This prepolymer is cross-linked with aromatic diamines having reduced reactivity with respect to isocyanate groups. The diamine reactivity is reduced by formation of a complex with certain alkali metal salts. This method is disadvantageous in that it is restricted to two special aromatic diamines and that it requires a separate process for the preparation of aromatic diamine and alkali metal salt complex.
Another method for controlling the velocity of the reaction between polyisocyanates and aromatic diamines utilizes an organic solvent as the reaction medium. Processes of this type have been described in U.S. Pat. No. 3,926,922 and published Japanese Patent Application No. 9195/70. The disadvantages of such processes include increased risk of fire and explosion and requirement of an expensive technological process for recovering the expensive and ecologically undesirable solvent.
German Auslegeschrift No. 1,122,699 discloses a process for the preparation of polyurethane elastomers in which liquid isocyanate prepolymers are cross-linked with mixtures of primary diamines and compounds having several hydroxyl groups. In this process, a pulverulent crystalline diamine is dispersed in a liquid polyether or polyester containing several hydroxyl groups or in castor oil. This diamine dispersion is introduced into the isocyanate prepolymer at a temperature below the melting point of the diamine. The reaction product is then cured at temperatures above the melting point of the diamine.
German Offenlegungsschrift No. 2,635,400 describes a process in which a finely ground diamine is suspended in a polyhydroxyl compound. The suspended diamine is then reacted with a polyisocyanate or a prepolymer containing isocyanate groups at a temperature below the melting point of the diamine. In this process, the aromatic diamine may also be stirred directly (in the form of a dry powder) into a prepolymer containing isocyanate groups. The reaction mixtures which have a long pot life are cured to produce polyurethane urea elastomers. Curing is preferably carried out at temperatures of from 80.degree. to 120.degree. C. and most preferably at 100.degree. to 110.degree. C. The curing temperature must, however, be below the melting point of the aromatic diamine.
Although those processes in which the diamines used as chain lengthening agents are reacted in a heterogeneous phase do have longer processing times, they also have serious toxicological disadvantages.